1. Field of the Invention
The invention pertains to micro-encapsulation in general and micro-encapsulation of buprenorphine in particular.
2. Prior Art
Buprenorphine is an opioid commonly used to treat withdrawal symptoms in patients attempting to cease the use of opiates such as heroin, oxycodone, hydrocodone, and morphine. There is some indication of its efficacy in treating cocaine addiction as well. Mello N K, Mendelson J H, Lukas S E, Gastfriend D R, Teoh S K, Holman B L. Buprenorphine Treatment of Opiate and Cocaine Abuse: Clinical and Preclinical Studies. Harv Rev Psychiatry 1993 September-October; 1(3): 168-83.
Buprenorphine is also used as an analgesic, and there is indication that it is well suited for treating certain types of depression. Bodkin J A, Zornberg G L, Lukas S E, Cole J O. Buprenorphine Treatment of Refractory Depression. Journal of Clinical Psychopharmacology 1995; 15:49-57.
Buprenorphine is generally administered via intramuscular injection, intravenous infusion, transdermal patch, or sublingual tablet. Buprenorphine is generally not administered orally. When compared to another common drug used to treat opiate addiction, methadone, buprenorphine is relatively long lasting. It has a mean elimination half-life of 34.6 hours. As a result, buprenorphine can often be administered every other day, whereas methadone typically must be administered at least once a day.
The need to administer any drug used for the treatment of narcotic addiction every day or every other day has the potential to cause problems. In the U.S., patients can be prescribed up to a thirty day supply of buprenorphine. This places the recovering addict in the position of having to decide whether to take his buprenorphine or not. The nature of opiate addiction being what it is, poor decisions in this regard by the recovering addict/patient are not uncommon.
One of the advantages of buprenorphine is the strength with which it binds to the receptors in the brain as compared to other opiates. One result of this is that when the patient has a sufficient amount of buprenorphine in his system, it will be difficult to impossible for him to achieve a high by taking other opiates. While on buprenorphine, taking illicit opiates becomes largely pointless for the recovering addict: withdrawal symptoms are substantially alleviated and the narcotic effects of the illicit opiate are blocked. This is believed to make it easier for the recovering addict to resist the temptation to resume consumption of opiates. However, to achieve these advantages, the recovering addict must have the buprenorphine in his system. If he neglects to take his buprenorphine, especially early in his treatment regimen, he can become particularly vulnerable to the pressures that can lead to resumption of illicit opiate consumption.
The present invention contemplates delivering buprenorphine in a micro-encapsulated form. As used herein, the terms micro-encapsulation and micro-capsules refer to particles having a diameter from about 1 micron to about 1000 microns. Micro-encapsulation of drugs is known. However, the process is usually quite inefficient. A large amount of drug is often lost during the encapsulation process. Losses as high as ninety percent are not uncommon.
Once formed, the micro-capsules will often not release the drugs they contain at a steady rate. Rather, a high rate of release is often experienced either initially or after the micro-capsules have been in an aqueous environment for some time. These “burst” effects can result in a significant amount of the drug becoming available to the patient at one time, which complicate the use of such micro-capsules as a drug delivery system.
In view of the foregoing, a system for delivering buprenorphine meeting the following objectives is desired.